GoRacer

Maybe a Mazdaspeed version? This will fix the low end lack of power and torque. I know it won't be as much HP as a turbo but I think it suits the RX-8 perfectly!

BryanH

Lack of low end torque? You need to drive a MKI MR2 for a couple weeks and then the RX-8's 110+ ft-lbs of torque at a mere 1,000 RPM will seem heavenly.

If torque is your bag you might like a V8.

GoRacer

I had two 1st gen MR2's. An '85 (allways problems)and an '86 (ran great). They were not as weak under 3k rpm's as the RX-7 is. However, they did ad a superchager to the 1st gen which prooves my point.

BryanH

But then the SC models didn't handle as well as the NAs, until you modified them. A popular swap is an SC motor into an early (lighter, better-handling) NA chassis.

I don't know which RX-7 you're referring to, but my experience driving/racing friends' RX-7s tells me the 7s have more low end grunt. The '85 GSL-SE had gobs of torque for a small engine, and the '86 FC Sport had a bit more than my MR2.

The 4AGE in my MR2 doesn't even wake up till 4k on the tach, then it pulls to the 7600 RPM rev limiter. Just off idle, there's no torque to be had at all. Only way to get a decent launch is to slip the clutch like crazy.

Anyway, getting back to the topic, I think the Renesis will have enough torque for my needs. My first car was a '71 Cuda with a 383, too, so I'm no stranger to the wonders of torque by the boatload.

Donny Boy

I would prefer to stay away from any type of forced induction for the RX-8. Forced induction creates too much stress on the engine. Prefer, I would, a 3 or even 4 rotor wankel. What think you.

Signed, Yoda.

Sputnik

I've got to agree with Bryan on that. As much as people would say that the FC lacked in torque, SOTP (a.k.a. "Butt Dyno"), it seems to pull more down low than the MKI MR2 NA.

---jps

GoRacer

I'm try to say that a supercharger matches better on the RX-8, better than it did on the MR2. Who would be crazy enough to take out the Supercharger in a MR2? ...what a waste!!!

Ovcourse the 1st gen RX-7 was torqy compare to the 3rg gen, what is the weight difference. The 2nd gen is still lighter than the 3rd. I never brought up 1st & 2nd gen's.

On the RX-7, power isn't available before 3k rpms. Call it torque, or flinstone feet, doesn't change the fact. A superchargers power is instant, no delay or lag like the turbo (even the sequential).

Since there should be more than one model and definately a Mazdaspeed version, then the high HP should be from a supercharger and not a turbo.

Sputnik

I disagree with that. There are two different types of SCs generally available today: The Roots type, and the centrifugal type. The limitations of both types are that they are only efficient in certain rpm ranges. The roots type operates best in lower rpms. Once it gets up to higher rpms, it creates more heat than boost. Since the rotary engine works better up in the higher rpms, you've somewhat handcuffed it from performing it's best at higher rpms. You've basically traded off high-end performance for low-end performance. The centrifugal type works best in higher rpms, so it would be of little help in the lower rpms, and it would make an already peaky engine even more peaky. The peak numbers for a centrifugal SC can seem impressive, but they are for such a narrow band that it is very misleading to the overall performance and capabilities of the engine.
Since an SC is only "efficient" in a limited rpm range, the fact that a rotary has such a high redline means that you will be outside of that "efficiency" range more often than in.

Meanwhile, a turbo is rpm independent. With the wastegate controlling the amount of boost, the turbo will be able to perform alot better throughout the extended rpm range.

Quote:

...A superchargers power is instant, no delay or lag like the turbo (even the sequential)...

As soon as you increase the piping distance between the SC and the intake manifold (and when you add an intercooler), you will add some lag to an SC setup. It wouldn't be huge, but it would be there.

---jps

GoRacer

Hmm, nice reply. I thought the SC work throughout the whole RPM range with the added benefit of low end power.

I know the rotary is capable of high end power. Take the Panspeed RX-8 redlining at 11k but on the "non"-ported RX-7 power falls off at 6500rpm which is not high at all.

BryanH

I think having tons of power below 3k RPMs isn't all that necessary. It's nice to have decent torque for around town, but I'm sure the standard RENESIS will have enough for the RX-8. When I want to get on it and go fast, I get the engine in the powerband and keep it there. Provided the '8's gears have good spacing, one should be able to keep the engine in the powerband at any speed above a few mph.

GoRacer

Ton's of power? Any power below 3k would be nice. The turbos don't kick in before 3k on the RX-7, so taking off is allways boggy unless your at 3k and then it lunges. At least make it drivable in stop & go city traffic. If it's more torque or more low end HP than the RX-7, then that's good enough (not asking it to be a Corvette).

wakeech

trade-off is the name of the game, 'cause if there's ever a perfect solution, everyone would be doing it...

just think about sports cars vs. sedans (saloons)... smaller, more powerful, sporty (duh), tading off comfort (sometimes), utility (in the usefulness sense, not enjoyment sense), and COST (excepting of course rediculously luxed-out sedans...)

the RX-8 tries to comprimize, but you could still make it more a sports car or more a sedan, but it would be by sacrificing characteristics one way or another...

same goes with mechanicals, especially in the engine... low end performance inhibits top end performance, and top end performance destroys bottom end performance (in ANY application)...
there are solutions which can be applied to minimize the trade-off (as in piston engines, multiple cam profiles, varying timing, and crap like that... or in rotaries variable sized intake ports), which as you can see all those who want to stay in the fore-front of competition have copied...
same goes with superchargers (roots vs. cetrifugal), or even turbos (bigger vs. smaller)... or even boosted vs. unboosted...
everything, when looking for maximizing one characteristic or another, is a trade-off...

MikeW

Roots--cheap cost, doesnt' require clutchable pulley as the Lyscholm does. lack luster performance, noise. Doesn't work well above single digit boost levels (<10 psi)
applicants--Eaton; GM 3800 SC; Ford F-150 Lighting, SVT Mustang; Nissan Frontier/Xterra; Jaguar XJR/XKR; Mercedes SLK, C-class hatchback

Inertial (often called centrifugal)--produces linear response, but exponential power, not positive displacement, noise.
Applicants--Vortech

Lysholm--expensive $, bad *** power all around, may work at up to 8-9K (actually compresses the air), requires disconnect clutch $.
Applicants--Mazda Millenia S; Mercedes AMG SL55, C32; Whipple

My vote would be for an inertial SC if the transmission/clutch is the limiting factor in the drivetrain (200 ft-lbs), otherwise a Lysholm (if less than $3000) or a Roots (<$1500)

Here are some links.
http://www.europeancarweb.com/tech/0105ec_supercharger/
http://www.vortechsuperchargers.com/
http://www.gadgetonline.com/Super.htm
http://www.whipplesuperchargers.com/homepage.html

Styjan

Not sure where you get your info from.

Official Mazda Specifications:

1981-84 RX-7
Curb Weight: 2,345lb
Output: 100bhp @ 6000rpm
Torque: 105lb-ft @ 4000rpm

1991 RX-7 T2
Curb Weight: 3,003lb
Output: 200bhp @ 6500rpm
Torque: 196lb-ft @ 3500rpm

1993 RX-7
Curb Weight: 2,789lb
Output: 255bhp @ 6500rpm
Torque: 217lb-ft @ 5000rpm

Plus, don't forget how cheap and easy it is to make an FD do over 350hp.

wakeech

how cheap and easy Styjan?? i love the FD, but don't know much about it (but i know a good deal about the FC... well, used to... :p)

Styjan

2-3 grand. Just a catback, intake and downpipe will give you a lot.

m477

I disagree. Look at all the 15+ year old turbocharged Saabs and Subarus with well over 100k miles on them. Turbo cars can last a long, long time if done right. Even the 3rd gen RX-7s can be made reliable, you just have to upgrade the entire cooling system and don't crank up the boost TOO much.

A 3- or 4-rotor will weigh too much, which will upset the weight distribution and handling would suck. Mazda's calling card with sports cars has always been being lighter and better handling than the competition. Which is much more important than increasing power IMO. Why do you think that the Miata has sold so well for so long while being underpowered?

I think the best solution would be just like they've done with the Mazdaspeed Protege, a small single turbo. I haven't driven one yet, but all the reviews I've read have been very positive - increased power over the entire rpm range with virutally no lag due to the small size and ceramic ball bearing.

Grimace

I would guesstimate that a 3 rotor motor would weigh less than adding a turbocharger, plumbing, intercooler, etc. to a 2-rotor motor.
But whatever, 250 HP is more than enough for me (and should be plenty for anybody).

Buger

While the 3 rotor has always been talked about as an engine for the rx-7, it never was put into production. It was rejected for the 3rd gen rx-7 mainly because of weight concerns. See the below excerpt from "Sports car color history - Mazda RX-7" by John Matras:

Kobayakawa knew that a triple would not only be a heavier engine, but its power output would require a stronger and therefore heavier chassis. A triple would also need more cooling and a bigger, heavier radiator. And as weight was added to the powerplant and accessories, even more weight would be needed for the chassis to support it, the brakes to stop it, and on and on. What Kobayakawa did not want was "Zevolution," that process that had changed the originally relatively spartan Datsun 240z into the mid-1980s boulevardier 300zx.

The renesis was developed because of it's ability to produce the Japanese limit of 280 ps without a turbo. It is amazing enough that the rx-8 could arrive weighing 2970, and it would be more amazing if it could arrive lighter than the previous rx-7. Remember that the 3rd gen rx-7 had many components of forged and sqeeze cast aluminum and they were used extensively in its suspension. For the current head of Mazda's r&d to say that the rx-8 could be lighter than the 3rd gen rx-7 is unbelievable.

If a new rx-7 ever makes it to our shores again, I believe we can count on it having a 2-rotor renesis, either tuned to be more powerful or with a turbo. Using the renesis for the rx-7 will also mean lower costs for both the rx-8 and rx-7. The focus of Mazda has always been on lightweight, great handling cars and they have a history of staking their position by building cars that are lighter and generally a little less expensive than their counterparts.

Two of the unique things about the rotary are its small size and its great power to weight ratio. The perfect road application for the rotary has always been a small, extremely lightweight car. You can trust that if Mazda can engineer the rx-8 to weigh 28** lbs, they can engineer a new rx-7 to be much lighter.

Brian

m477

Come on, you actually think a turbo/intercooler would weigh as much as half of the entire engine? How much weight did the Mazdaspeed protege gain from being turbocharged? Not a whole lot, I believe.

Also pretty much directly analogous to this case - the 4-cyl turbo (w/intercooler) Volkswagen GTi weighs a good deal less than the VR6 version.

Plus the modability of turbo cars is great. I'm not really into dragging, but I think that it would be cool just knowing that people out there are running 10s and spanking cocky V-8s with Renesis-powered cars. In other words, making people respect (and fear) the latest generation of rotary-powered cars, just like TIIs and FDs have done for years.

Sputnik

Remember, it wouldn't be half of the entire engine, it would only be another rotor and housing. Then you have to consider the manifold, turbo, wastegate, IC, all sorts of tubing, etc. etc. Depending on the setup, it could be close.

---jps

rpm_pwr

Of all the turbo variants of cars I can think of, the turbo version weighed about 80-140kg more. That always included bigger brakes, oil cooler and radiator and in all but one example a stronger transmission.


-pete

m477

Here's some real world data for you:
Volkswagen Jetta:
NA 4-cyl: 2,934lbs
Turbo 4-cyl: 2,974lbs

Difference = 40lbs

Yeah, some turbo cars gained lots of weight, but that's only because the NA versions were slow and weak as hell. For example the 3000gt. The RX-8 will be fast even without a turbo, but will be even faster with one. I don't get why everyone seems so hostile and upset at the idea of a turbocharger. I mean, did you people get mad when the mazdaspeed protege came out? The mazdaspeed version is better in every way, and the turbo is an important part of the package IMO. And if a 4th gen 7 comes out, it sure as hell better have a turbocharger. It just wouldn't be a 7 without one. In Japan, the first turbo RX-7 came out it 1982, and ALL j-spec RX-7s have been turbo since 1985. Turbos are an important part of the rotary heritage, I hope they don't abandon that with the newest generation.

Quick_lude

If it can be made reliable, I'm all for more power. But the increased cost would push the price to another level.. Could the RX-8 sell/compete there?

fuz

I just don't like the sudden onrush of power from a turbo. I find it annoying when applying throttle out of a corner, only to slide the tail a bit too much from the uncontrolable power. An NA power curve is much more predictable. Less power, but much easier to use.

Maybe I'm just not a good enough driver.